Well, a correction first: Hijnx is only displaying the photos. They are not in your server and he only references them from here with HTML code.
On the other hand, you can upload images to your server, first by browsing for the file you want to upload. This is done by clicking in the "Browse" button and navigating in the window that pops up. Once you have found the file, click once on it and then hit OK. Last step is to click on the "post" button.
Try to upload small images only (640 X 400 pixels max) since if the photo is bigger than the screen, the forum format won't be displayed properly...
(Gee, I guess I'm Chicken Wings' official geek now, right?)